Before resetting, you should check:
You have changed fresh batteries for the mic, but there is still interference or disconnection.
You have changed the frequency of the mic, but it still cannot pair with the receiver.
If you have multiple K040 mic sets, and some don't work.
How to reset:
Turn OFF the mic, keep the receiver on. Keep them close to each other.
Press and hold the Set and Power buttons down simultaneously until the " ---- " appears on the screen of the mic. Release both buttons.
When the mics pair with the receiver, the RF indicators will bounce when you speak into the mics. The frequency on the receiver will be the same as the frequency on the receiver.
When pairing your Fifine mic system, make sure only ONE Fifine receiver is turned on and only ONE microphone is in pairing mode at a time. Otherwise, the specific mic will pair with all the receivers that are powered on. Please don't be away from the receiver more than 10 feet when you reset the mic set.
You can refer to the video from 4:27 to 5:20.